Well, I agree with your math and your assessment of the situation. I was perhaps being generous by referencing a third, a third, and a third. Also, the requirement for it to be P3 is quite a thing to saddle local municipalities with in return for that 25%, as you say.
You have to remember that, while year after year local cities and regions are being saddled with more and more financial responsibilities, at the same time they're not able gather more municipal taxes. Also, we've seen what happens when they try to implement new tax forms, like with our Vancouver transit plebiscite. Even in a place as transit-friendly as the Vancouver region, the transit plebiscite has been a nightmare both politically and practically.
I think you're describing the problem well. But it's even worse in the sense of how much of what used to be provincial and federal responsibilities through tax incentives for rental housing, or various programs for daycare operations, and such, has been downloaded to municipalities over the years. I used to say that municipalities were being squeezed economically. Now I say they're being crushed.